It is generally assumed that verbal abilities are more resistant to the effects of increasing age than nonverbal abilities. Such a differential loss of nonverbal as opposed to verbal, abilities has important implications for theoretical models of aging, for the optimal utilization of the skills of older individuals, and for the identification of cognitive abilities that are affected by disease processes which occur with higher frequency among older individuals. However, evidence for this differential age decrement is not based on totally valid considerations. It may reflect a failure to establish strictly comparable tests of verbal and nonverbal information processing skills. Our objective is to utilize a reaction time paradigm to provide a stringent experimental test of verbal and nonverbal processes in elderly persons. In so doing, the specific objective is to evaluate the relative degree of impairment of multiple cognitive functions within age groups so that specific mental functions, e.g., data storage, selective attention, information retrieval, information manipulation, response selection, and short term "working memory processes" which may contribute to disproportional handicap in older persons may be identified. A second objective is to explore the relation of verbal and nonverbal information processing ability to cortical asymmetry and the interaction of left and right cerebral hemispheres.